nginx rewrite rule to remove - and _ - redirect

Question

i need a nginx rewrite rule for the following problem:
I have Urls that include several hyphen and eventually underscores
Example request: http://www.example.com/cat/cat2/200-AB---a-12_12-123.312/cat-_-cat/cat/dog---I
would give a 404 error
so in need a 301- redirect to:
http://www.example.com/cat/cat2/200-AB-a-12-12-123.312/cat-cat/cat/dog-I
So all underscores should be replaced with hyphens and there should be only one hyphen a time.
short version:
replace --- with - and replace _ with -
but by replacing _ with - this -_- will become --- and rule one would have to be called again.
Is it possible to to that in one rule? and if not how to do it any other way :)i have absolutely no idea how to do that with nginx
any help appreciated :)

Answer 1

% nginx -c $PWD/test.conf
% curl -I localhost:8080/cat/cat2/200-AB---a-12_12-123.312/cat-_-cat/cat/dog---I
HTTP/1.1 301 Moved Permanently
Server: nginx/1.3.13
Date: Wed, 20 Feb 2013 00:09:50 GMT
Content-Type: text/html
Content-Length: 185
Location: http://localhost:8080/cat/cat2/200-AB-a-1212-123.312/cat-cat/cat/dog-I
Connection: keep-alive
% cat test.conf
events { }
#error_log logs/error.log debug;
http {
server {
listen 8080;
location /cat/cat2/ {
# replace up to 3 inconsecutive
# uderscores per internal redirect
rewrite "^(.+?)_+(?:(.+?)_+)?(?:(.+?)_+)?(.+)$" $1$2$3$4 last;
# replace up to 3 inconsecutive multiple
# hyphens per internal redirect
rewrite "^(.+?-)-+(?:(.+?-)-+)?(?:(.+?-)-+)?(.+)$" $1$2$3$4 last;
return 301 $uri;
}
}
}